1. Technical Field
This disclosure relates to therapeutic medical applications of ultrasound, and in particular to a method for promoting healing of the sternum using therapeutic ultrasound.
2. Description of the Related Art
Referring to FIG. 1, the sternum 10 is a heavily vascularized tissue positioned in the chest 12 between the lateral sets of ribs 14, 16 forming the rib cage. Being composed of both bone and cartilage and heavily vascularized, the sternum 10 has unique characteristics with respect to the skeletal structure of humans.
During conventional open heart surgery, the sternum is typically cut, as shown in FIG. 2, by a saw or by an electrocautery device to separate and spread the rib cage open to expose the heart, as shown in FIG. 3. The cut 18 is generally positioned longitudinally along the length of the sternum 10 for maintaining the conjunction of the portions 20, 22 of the sternum 10 with the respective sets of ribs 14, 16.
When the sternum is cut in such surgical procedures, the resultant bleeding from the sternum may be significant due to its heavy vascularization. Typically, the bleeding is stopped during the surgery by cautery procedures or by application of bone wax; i.e. wax or wax-like substances for sealing the cut and severed blood vessels.
After completion of the surgical procedure, the chest cavity is closed, which involves positioning and re-approximating the portions of the cut sternum together for subsequent healing, using, for example, stainless steel wires 24-28 and/or bands, as shown in FIG. 4, for affixing the sternum portions 20, 22 together and/or for constricting the patient""s chest to force the sternum portions to be adjacent. For example, U.S. Pat. Nos. 4,802,477 and 5,330,489 disclose sternum closure devices for retaining split portions of human tissue such as the sternum in adjacent contacting relation to promote healing. Other devices or structure may be used to secure the sternum portions together during healing; for example, U.S. Pat. No. 5,163,598 describes a sternum stapling apparatus for stapling the sternum portions together with a bone staple.
U.S. Pat. No. 5,139,498 describes a device consisting of a plate having two flat longitudinal parallel anchoring members with through-holes for threading wire to hold the sternum portions together. U.S. Pat. No. 4,792,336 describes a surgical repair device composed of absorbable material which is braided and used for securing tissue together. U.S. Pat. Nos. 4,792,336 and 5,139,498 are incorporated herein by reference.
Such devices described above may be disposed adjacent to the approximated sternum portions and internally located after the patient""s chest is closed and sutured. Such devices may be permanent or may be removed at a later date after the sternum healing has been sufficiently effected.
Post-operative complications to the union of the sternum portions may be caused due to the cautery or bone wax which, in stopping the bleeding during the surgery, prevent proper healing after the surgery. Other causes of post-operative complications of the cut sternum include ventilation of the chest cavity; i.e. breathing. Due to the position of the sternum between the ribs and over the chest, breathing causes stress and strain on the sternum portions, preventing proper healing.
In addition, as the muscles of the chest are connected to other muscles such as those to the abdomen, upper limbs, and head, muscular movement also may contribute stress and strain on the sternum portions during healing.
Furthermore, known devices such as wires and bands as well as plates and muscle clamps have been used to secure the sternum portions together. The use of these devices have met with some success to promote healing of the sternum. However, such devices have been found to loosen, such as wire 26, and even migrate, such as wire 28, thus allowing the sternum portions 20, 22 to separate, as illustrated in FIG. 4.
Accordingly, the incidence of dehiscence of the sternum; i.e. the failure of the sternum to heal, which results or causes relatively massive infection to the sternum and surrounding region, is of significant concern. In turn, such infections further reduce the healing of the sternum by reducing the ability of the sternum portions to join and fuse to each other during proper healing.
Further, due to movement of the sternum portions 20, 22 caused by muscular activity and breathing, as well as strain to the spinal joints and intercostal joints 30, 32, shown in FIG. 4, from the separation of the ribs, in addition to nerve exposure due to the surgery, serious pain may occur from even regular activity and movement.
It is generally known that complications from such heart surgery and post-operative effects, such as dehiscence of the sternum, may occur at a frequency of about 0.5% to about 7.0% of patients undergoing such heart surgery. Of such patients experiencing complications, mortality occurs in about 14% of such cases.
Post-operative complications associated with the failure of the sternum to heal properly are generally most common among the elderly, diabetics, obese people, smokers, people who have used steroids, patients having chemotherapy or radiation therapy, and patients who have lung disease or lung surgery. In particular, for the elderly who may more often require heart, lung, or other chest surgery, complications in sternum healing generally have an increased likelihood since the sternum is about 1 cm to about 1.5 cm. thick, but such thickness reduces in relation to one""s age.
Although known devices are indeed effective for promoting healing of a cut sternum, the frequency of complications and mortality is still considerable. In addition, such devices are limited in effectiveness, as the sternum portions may separate despite such devices, or in fact because such devices may not operate properly. For example, a bone staple holding the sternum portions together may loosen due to the natural and regular breathing and other muscular movement of the sternum and ribs. Further, such known devices for sternum healing may require replacement or adjustment to compensate for any maladjustment or ineffectiveness.
Accordingly, a need exists for promoting effective sternum healing; for example, a device and/or a method which heals the sternum, individually or in conjunction with such devices known in the art, including wires and bands.
A need also exists for a device and/or a method for promoting sternum healing which is conveniently applied, and which may be applied with less expense. Such a device and/or method may also be non-invasive, to allow recovering patients to avoid additional surgery to replace or adjust known sternum healing devices and methods.
The application of ultrasound to accelerate the healing of tissue and bone has been described, for example, in commonly assigned U.S. Pat. No. 4,530,360 to Duarte and U.S. Pat. No. 5,520,612 to Winder et al. For example, as described by the Duarte patent, ultrasound may be applied to bone, with ultrasonic frequencies of about 1.5 MHz with pulse widths which vary between 10 xcexcs and 2,000 xcexcs, and with pulse repetition rates which vary between 100 and 1,000 Hz. Such applications of ultrasound have been shown to accelerate the normal healing process of bone fractures, pseudoarthroses, and the like. Heretofore, ultrasound has not been applied to promote the post-operative healing of the sternum.
It is recognized herein that the application of therapeutic ultrasound to the sternum accelerates the healing of the sternum, and so minimizes dehiscence and other complications of surgery involving cutting of the sternum.
A method for sternum healing of a patient is disclosed which includes the steps of positioning an ultrasound application device substantially adjacent to a sternum having approximated portions; and applying ultrasound to the approximated portions of the sternum for promoting healing of the approximated portions together.
The ultrasound application device includes a transducer for generating ultrasound for application to approximated portions of the sternum for promoting healing of the approximated portions together; and a base for positioning the transducer substantially adjacent to the sternum. In one embodiment, an ultrasound diverging lens is included which is disposed between the transducer and the sternum for acoustically diverging the ultrasound to flood the approximated portions of the sternum for healing thereof.
In another embodiment, a plurality of transducers are included which are positioned in a plurality of recesses of the base along a longitudinal length of the approximated portions of the sternum and substantially adjacent to the skin over the sternum for applying the ultrasound along the longitudinal length of the approximated portions of the sternum.
A ring may be included which is connected to the base and adapted to be positioned and secured about the neck of the patient. The ring may be woven and/or incorporated in a tie.
In another embodiment, a metal strip is included which is operatively connected to the transducer, and which responds to signals from the transducer for generating the ultrasound and for applying the ultrasound to the sternum. The metal strip may be implanted within the patient substantially adjacent to the sternum.
In another embodiment, the ultrasound application device may operate in conjunction with a mesh implanted in the patient substantially adjacent to the sternum, in which the mesh responds to ultrasound applied thereto to promote healing of the sternum.